Projected changes in rainfall and temperature over Greater Horn of Africa (GHA) in different scenarios In Support of: Planning for Resilience in East Africa through Policy, Adaptation, Research, and Economic Development (PREPARED) Project March 2016 1
1. Introduction Global Climate Models (GCMs) forced with scenarios of the evolution of concentrations of greenhouse gases (GHG) and aerosols, are the fundamental tools for projecting climate change. However, because of their high complexity and the need to perform very long simulations, GCM simulations are very demanding in computational resources and are performed at relatively coarse horizontal resolution. Due to this, they are not necessarily capable of capturing the detailed processes associated with regional local climate variability and changes that are required for accurate regional and national climate change assessments. It is thus not surprising that GCMs provide information at spatial scales coarser than those typically required for developing reliable adaptation and mitigation strategies. This limitation of GCMs can be overcome by using regional climate models (RCMs) by dynamically downscale the coarse resolution of GCM outputs to scales more suited to particular end-users over specific geographic regions of interest. RCMs use the information derived from GCM simulations to define the surface and lateral boundary conditions. This enables RCMs to better represent the topographical details, coastlines, and land-surface heterogeneities, and hence to more faithfully reproduce small-scale processes and details that are essential to developing reliable climate change impact assessment and adaptation policies. Recently, the Coordinated Regional Climate Downscaling Experiment (CORDEX) program, initiated by the World Climate Research Program, provided the opportunity for generating highresolution regional climate projections, which can be used to assess the future impacts of climate change at regional scales (Giorgi et al. 2009). In this report, simulated data from the Rossby Center regional atmospheric model (RCA4) driven by the Earth system version of the Max Planck Institute for Meteorology (MPI-ESM-LR) coupled global climate model is used from the on-going CORDEX project. The model was integrated into the CORDEX-Africa domain (see Nikulin et al. 2012, Endris et al. 2013), with a horizontal grid spacing of 0.44 degrees. The historical simulations are forced by observed natural and anthropogenic atmospheric composition covering the period from 1950 until 2005, whereas the projections (2006 2100) are forced by Representative Concentration Pathways (RCPs). The choice of the RCA model driven MPI-ESM-LR for this analysis was based primarily on the availability of the model outputs for the three different scenarios (RCP2.6, RCP4.5 and RCP8.5), as the other model runs were available for only one or two of the three scenarios. Moreover, a recent assessment study (Endris et al. 2015) has shown that the RCA model run 2
driven by MPI-ESM-LR better reproduces the large-scale signals such as the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) in the historical period over the eastern Africa region than RCA model run driven by the other GCMs. 2. Description of the three climate scenarios used in this report The simulations used for the projections are forced by the Representative Concentration Pathways (RCPs), which are based on radiative forcings (globally radiative energy imbalance) measured in W m -2 by the year 2100 (Moss et al. 2010). In this report, three RCPs are used, namely, RCP2.6, RCP4.5 and RCP8.5, which represent the low, mid and high-level emission and concentration scenarios, respectively. The RCP2.6 emission and concentration pathway, also referred to as RCP3PD (Peak and Decline), represents a peak in radiative forcing at ~3 W/m 2 (~490 ppm CO2) by the mid-twenty-first century and then a decline to 2.6 W/m 2 by 2100. This scenario assumes optimistic mitigation measures and that the increase in the global average temperature will be limited below 2 O C. RCP4.5 is a medium level concentration pathway that is assumed to stabilize radiative forcing at 4.5 W/m 2 (~650 ppm CO2) and that this value will not be exceeded by the year 2100. The RCP8.5 pathway represents a high concentration pathway in which radiative forcing is assumed to reach 8.5 W/m 2 by the year 2100 (~1370 ppm CO2) and then continues to rise thereafter. The RCP8.5 socio-economic pathway is characterized by rapidly rising population and relatively slow income growth with modest rates of technological change and energy intensity improvements, leading in the long term, to high-energy demands and GHG emissions in the absence of climate change policies (Riahi et al., 2011). Figure 1: Concentration of carbon dioxide (CO2) across the three RCPs. The dotted lines indicate three of the SRES marker scenarios. Source: Van Vuuren et. al. (2011). 3
3. Results and discussion The projected changes in rainfall, maximum and minimum temperatures based on the RCP 2.6, RCP 4.5 and RCP 8.5 scenarios have been analysed for four future time slices 2020s (2006-2035), 2030s (2016-2045), 2050s (2036-2065) and 2070s (2055-2085) to provide information on the expected magnitude of the climate response over each time window. The period 1971-2000 is considered as a reference for the present climate. The projected climates change signals for each time window are calculated as the difference between the future time windows (averages calculated over 3o years) and the reference period. For example, the rainfall change by 2070s is computed based on the difference in average rainfall between 2055-2085 and the reference period (1971-2000). This is because the conditions prevailing in any individual year will be strongly affected by the natural climatic variability to reliably predict. Rainfall Figures 2a-d show the projected changes in the annual and seasonal rainfall components over the Greater Horn of Africa (GHA) for the 2020s, 2030s, 2050s and 2070s under the three scenarios, compared to the reference period (1971 2000). The projected changes in the annual rainfall component under each of the three different scenarios and time windows show relatively little change compared to the projected changes in the seasonal rainfall components. The short rains (OND period) are projected to increase over most parts of the region under all the three scenarios (>50%). By contrast, the long rains (MAM) and JJAS are projected to decease over most part of the region (10-70%) but slight increase (10-25%) in MAM rains over the southeastern part Lake victoria basin. The projected annual rainfall shows a tendency to increase over the south-eastern part of the region and decrease over north-western part of the domain. Maximum temperature The projected changes in the maximum temperature component for the three scenarios (RCP2.6, RCP4.5 & RCP8.5) in the 2020s, 2030s, 2050s and 2070s periods compared to the reference period (1971 2000) are shown in Figures 3a-d. Unlike for rainfall, the projected temperature changes for the three different scenarios and time windows show relatively large changes compared to the projected changes in the seasonal components. By 2020, annual maximum temperatures are anticipated to be 0.5 to 1.0 C higher under the RCP2.6 scenario but 0.5 to 1.5 C higher under the RCP4.5 and RCP8.5 scenarios over most parts of the region, with slightly less warming apparent in some coastal areas. The expected warming extent is greatest 4
during MAM and JJAS seasons and least during the short rains (OND). By 2030, maximum temperatures during MAM, JJAS and throughout the year (Annual component) will likely increase by 1.0 to 2.5 C over most parts of the region but with spatial variation similar to those for 2020. By 2050, annual maximum temperatures are expected to be 1.0 to 2.0 C higher under the RCP2.6, 1.5 to 2.5 C higher under the RCP4.5 and 2.5 to 3.5 C higher under the RCP8.5 scenarios over most parts of the GHA, with slightly less warming expected in some coastal areas. The greatest potential warming will likely occur in the JJAS and MAM. In the far future (2070), projected annual maximum temperatures will likely be 0.5 t0 1.5 C higher under the RCP2.6 scenario, which is notably smaller than the changes anticipated by 2050. This is due to the reduction in radiative forcing expected toward the end of the century due to mitigation measures under the RCP 2.6 scenario. In contrast, under the RCP8.5 scenario, the expected annual warming will likely result in temperatures 3.5 t0 5 C higher than the reference period, with far greater warming expected during MAM and JJAS. Minimum temperature The projected changes in the minimum temperatures through time for the three scenarios are shown in Figures 4a-d. The results suggest that there will likely be a greater increase in the minimum than the maximum temperatures in future. By 2020, annual minimum temperatures will likely be 0.5 to 1.5 C higher under the RCP2.6 and the RCP4.5 scenarios, but 1.0 to 2.0 C higher under the RCP8.5 scenario over most parts of the GHA region. By 2030 and 2050, almost all the GHA region will likely be 1.0 to 3.0 o C warmer than the base period, with the greatest warming expected during the MAM and JJAS under the RCP8.5 scenario. By 2070, the projected increase in the annual minimum temperatures will likely be 4 to 5 o C higher under the RCP8.5 scenario relative to the base period. 4. Key findings Rainfall: The sign and intensity of projected rainfall changes in different scenarios and time windows show relatively little change compared to projected rainfall changes in different seasons. OND rainfall projected to increase across GHA, while MAM and JJAS rainfall tends to decrease over most part of the region. Annual rainfall changes are projected to increase over eastern and south-eastern part of the region, and decrease in the rest of the region. 5
Temperature: All areas of the GHA will get warmer in future; the warming is greater in MAM and JJAS than in OND. There will likely be a greater increase in the minimum than the maximum temperatures in future. The average regional annual maximum and minimum temperature rises, for high emission scenario (RCP8.5), in the 2050s and 2070s will be between 3 and 5 C. 5. References: Endris, H. S., Lennard, C., Hewitson, B., Dosio, A., Nikulin, G., & Panitz, H. J. (2015). Teleconnection responses in multi-gcm driven CORDEX RCMs over Eastern Africa. Climate Dynamics, 1-26. Endris, H. S., Omondi, P., Jain, S., Lennard, C., Hewitson, B., Chang'a, L.,... & Panitz, H. J. (2013). Assessment of the performance of CORDEX regional climate models in simulating East African rainfall. Journal of Climate, 26(21), 8453-8475. Giorgi, F., Jones, C., & Asrar, G. R. (2009). Addressing climate information needs at the regional level: the CORDEX framework. World Meteorological Organization (WMO) Bulletin, 58(3), 175. Nikulin, G., Jones, C., Giorgi, F., Asrar, G., Büchner, M., Cerezo-Mota, R.,... & van Meijgaard, E. (2012). Precipitation climatology in an ensemble of CORDEX-Africa regional climate simulations. Journal of Climate, 25(18), 6057-6078. Riahi, K., Rao, S., Krey, V., Cho, C., Chirkov, V., Fischer, G.,... & Rafaj, P. (2011). RCP 8.5 A scenario of comparatively high greenhouse gas emissions. Climatic Change, 109(1-2), 33-57. Moss, R. H., Edmonds, J. A., Hibbard, K. A., Manning, M. R., Rose, S. K., Van Vuuren, D. P.,... & Wilbanks, T. J. (2010). The next generation of scenarios for climate change research and assessment. Nature, 463(7282), 747-756. Van Vuuren, D. P., Edmonds, J., Kainuma, M., Riahi, K., Thomson, A., Hibbard, K.,... & Masui, T. (2011). The representative concentration pathways: an overview. Climatic change, 109, 5-31. 6
Figures: Figure 2a: Projected rainfall changes over GHA by 2020s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 7
Figure 2b: Projected rainfall changes over GHA by 2030s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 8
Figure 2c: Projected rainfall changes over GHA by 2050s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 9
Figure 2d: Projected rainfall changes over GHA by 2070s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 10
Figure 3a: Projected maximum temperature changes over GHA by 2020s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 11
Figure 3b: Projected maximum temperature changes over GHA by 2030s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 12
Figure 3c: Projected maximum temperature changes over GHA by 2050s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 13
Figure 3d: Projected maximum temperature changes over GHA by 2070s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 14
Figure 4a: Projected minimum temperature changes over GHA by 2020s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 15
Figure 4b: Projected minimum temperature changes over GHA by 2030s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 16
Figure 4c: Projected minimum temperature changes over GHA by 2050s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 17
Figure 4d: Projected minimum temperature changes over GHA by 2070s in annual (1 st column), MAM (2 nd column), JJAS (3 rd column), OND (4 th column). Each row corresponds to emission scenarios: RCP2.6 (1 st row), RCP4.5 (2 nd row) and RCP8.5 (3 rd row). 18